Experimental Section

Nitric oxide reactivity

2.4 Experimental Section

2.4.1 Materials and methods

All reagents and solvents of reagent grade were purchased from commercial sources and used as received except specified. Acetonitrile was distilled from calcium hydride.

Deoxygenation of the solvent and solutions was effected by repeated vacuum/purge cycles or bubbling with nitrogen for 30 minutes. NO gas was purified by passing through KOH and P2O5 column. UV-visible spectra were recorded on a Perkin Elmer Lambda 25 UV- visible spectrophotometer. FT-IR spectra of the solid samples were taken on a Perkin Elmer spectrophotometer with samples prepared as KBr pellets. Solution electrical conductivity was measured using a Systronic 305 conductivity bridge. ¹H-NMR spectra

Chapter 2

36

were recorded in a 400 MHz Varian FT spectrometer. Chemical shifts (ppm) were referenced either with an internal standard (Me4Si) or to the residual solvent peaks. The X- band Electron Paramagnetic Resonance (EPR) spectra were recorded on a JES-FA200 ESR spectrometer, at room temperature and 77 K with microwave power, 0.998 mW;

microwave frequency, 9.14 GHz and modulation amplitude, 2. Elemental analyses were obtained from a Perkin Elmer Series II Analyzer. The magnetic moment of complexes was measured on a Cambridge Magnetic Balance.

Single crystals were grown by slow diffusion followed by slow evaporation technique. The intensity data were collected using a Bruker SMART APEX-II CCD diffractometer, equipped with a fine focus 1.75 kW sealed tube MoKα radiation (λ, 0.71073 Å) at 273(3) K, with increasing ω (width of 0.3° per frame) at a scan speed of 3 s/frame. The SMART software was used for data acquisition. Data integration and reduction were undertaken with SAINT and XPREP software.²⁶ Structures were solved by direct methods using SHELXS-97 and refined with full-matrix least squares on F² using SHELXL-97.²⁷ All non-hydrogen atoms were refined anisotropically. Structural illustrations have been drawn with ORTEP-3 for Windows.²⁸

2.4.2 Synthesis of ligands Synthesis of L1

The ligand L1 was reported earlier.²⁹ To a solution of pyridine-2-carboxaldehyde (2.14 g, 20 mmol) in 20 ml methanol was added ethylenediamine (0.60 g, 10 mmol) into a 50 ml round bottom flask equipped with a stirring bar. The solution was refluxed for 5 h. The resulting reddish-yellow solution was then reduced by NaBH4 (1.52 g, 40 mmol). Removal of solvent under reduced pressure affords a crude mass. It was dissolved in water (50 ml) and extracted with chloroform (50 ml × 4 portion). Organic part was dried under reduced

δ

135.1, 147.6 and 157.6. ESI-Mass (m+1): Calcd. 243.32; Found, 243.04.

Synthesis of L2

Ligand L₂ was prepared following the same procedure used for L₁ from the reaction of pyridine-2-carboxaldehyde and propylenediamine. Yield: 2.18 g, ~85%. Elemental analyses for C15H20N4: Calcd. (%): C, 70.28; H, 7.86; N, 21.86. Found (%): C, 70.23; H, 7.85; N, 21.94. FT-IR in KBr: 2791, 1591, 1475, 1430, 1167, 767 cm^-1. ¹H-NMR (400 MHz, CDCl3) δppm: 1.75-1.79 (2H), 2.70-2.77 (4H), 3.90 (4H), 7.13-7.16 (4H), 7.28-7.30 (2H) 7.60-7.64 (2H), 7.52-7.54 (2H). ¹³C-NMR (100 MHz, CDCl3) δppm: 29.8, 47.5, 54.8, 121.5, 121.9, 136.0, 148.8 and 159.4. ESI-Mass (m+1): Calcd. 257.35; Found, 257.04.

Synthesis of L3

L3 was synthesized by following the reported procedure.³⁰ A solution of 1.21 g (5 mmol) of L1 and 0.54 g (5 mmol) of pyridine-2-carboxaldehyde in 20 ml of diethyl ether was stirred at room temperature for 3 h to afford white precipitate. The solid obtained after filtration was washed with diethyl ether. In a 250 ml flask, 1.66 g of the solid (5 mmol) was dissolved in 50 ml methanol and to this 0.315 g (5 mmol) of NaBH3CN dissolved in 4 ml methanol and 0.77 ml (10 mmol) of CF3CO2H were added. The solution was stirred at room temperature for 8 h. To this NaOH solution (15%, 50 ml) was added and then extracted with CH2Cl2 (4 × 100 ml portions). Removal of solvent under vacuum affords L3

Chapter 2

38

as yellow oil. Yield: 1.26 g, ~76%. Elemental analyses for C20H23N5: Calcd. (%): C, 72.04;

H, 6.95; N, 21.00. Found (%): C, 72.11; H, 6.95; N, 21.10. FT-IR in KBr: 2916, 2786, 1583, 1477, 1432, 765 cm^-1. ¹H-NMR (400 MHz, CDCl3) δppm: 2.16 (1H) 2.78 (4H), 3.82 (6H), 7.12-7.15 (4H), 7.27 (1H), 7.51 (1H), 7.59-7.65 (4H), 7.49 (1H). ¹³C-NMR (100 MHz, CDCl3) δppm: 48.8, 54.0, 54.8, 54.9, 60.5, 121.8, 121.8, 121.9, 122.2, 122.2, 123.1, 136.3, 136.4, 148.8, 149.1, 159.4 and 159.6. ESI-Mass (m+1): Calcd. 334.43; Found, 334.78.

Synthesis of L4

Ligand L₄ was prepared following the same procedure used for L₃ from the reaction of 1- methylimidazole-2-carboxaldehyde with L1. Yield: 1.21g, ~72%. Elemental analyses for C19H24N6: Calcd. (%): C, 67.83; H, 7.19; N, 24.98. Found (%): C, 63.77; H, 7.21; N, 24.89.

FT-IR in KBr: 2922, 2803, 1593, 1471, 1432, 1141, 767 cm^-1. ¹H-NMR (400 MHz, CDCl3) δppm: 2.71-2.82 (4H) 3.58 (3H), 3.75-3.79 (6H), 6.75 (1H), 6.88 (1H), 7.12-7.16 (2H), 7.25-7.36 (2H), 7.58-7.63 (2H), 8.49-8.53 (2H). ¹³C-NMR (100 MHz, CDCl3) δppm: 32.6, 46.4, 48.8, 53.8, 54.6, 59.9, 121.3, 121.6, 121.8, 121.9, 123.2, 126.7, 136.1, 136.1, 148.7, 148.8, 148.9, 158.8 and 159.5. ESI-Mass (m+1): Calcd. 337.43; Found, 337.22.

2.4.3 Synthesis of complexes

The complexes have been synthesized following a general experimental procedure of the reaction of [Cu^II(H₂O)₆](ClO₄)₂ with equivalent quantity of the respective ligand. The details are given for complex 2.1.

Synthesis of complex 2.1

[Cu^II(H2O)6](ClO4)2 (1.85 g, 5 mmol) was dissolved in 10 ml distilled acetonitrile. To this solution, L1 (1.21 g, 5 mmol) was added slowly with constant stirring. The color of the solution turned into greenish-blue. The stirring was continued for 1h at room temperature.

(Ω M cm), 244. µobs, 1.56 BM.

Synthesis of complex 2.2

Complex 2.2 was synthesized from [Cu^II(H2O)6](ClO4)2 (1.85 g, 5 mmol) and L2 (1.28 g, 5 mmol). Yield: 2.12 g, ~82%. UV-vis. (acetonitrile): λmax, 618 nm (ε, 166 M^-1cm^-1). X- Band EPR (in methanol at 77 K): g║, 2.270; g⊥, 2.061; A║, 164 × 10^-4 cm^-1. FT-IR in KBr:

3166, 2866, 1608, 1120, 1082, 765, 625cm^-1. Molar conductivity in acetonitrile: ΛM (Ω^-1M^-

1cm²), 236. µobs, 1.51 BM.

Synthesis of complex 2.3

Complex 2.3 was synthesized from [Cu^II(H2O)6](ClO4)2 (1.85 g, 5 mmol) and L3 (1.67 g, 5 mmol). Yield: 2.62g, ~88%. UV-vis. (acetonitrile): λmax, 672 nm (ε, 208 M^-1cm^-1). FT-IR in KBr: 3238, 3077, 1610, 1484, 1144, 1108, 1088, 771, 624 cm^-1. X-band EPR (in methanol at 77 K): g║, 2.207; g_⊥, 2.013; A║, 158 × 10^-4 cm^-1. Molar conductivity in acetonitrile: ΛM (Ω^-1M^-1cm²), 205. µobs, 1.56 BM.

Synthesis of complex 2.4

Complex 2.4 was synthesized from [Cu^II(H2O)6](ClO4)2 (1.85 g, 5 mmol) and L4 (1.68 g, 5 mmol). Yield: 2.54 g, ~85%. UV-vis. (acetonitrile): λmax, 640 nm (ε, 173 M^-1cm^-1). The X- Band EPR (in methanol at 77 K): g║, 2.230; g_⊥, 2.035; A║, 138 × 10^-4 cm^-1. FT-IR in KBr:

Chapter 2

40

3255, 1611, 1447, 1144, 1108, 1089, 767, 626 cm^-1. Molar conductivity in acetonitrile: ΛM

(Ω^-1M^-1cm²), 236. µobs, 1.54 BM.

2.4.4 Isolation of L1/

Complex 2.1 (0.252 g, 0.5 mmol) was dissolved in 10 ml of distilled and degassed methanol. To this solution one equivalent of the sodium ethoxide was added and then excess of NO gas was purged. The resulting colorless solution was stirred for 1 h at room temperature. After removing the excess NO by several cycles of vacuum/purge, 10 ml of degassed benzene was added to this under dinitrogen atmosphere. The reaction mixture was kept in freezer for overnight. The L1/

-perchlorate was found to be precipitated out.

Yield: 0.133g, ~70%. Elemental analyses for C14H22N5ClO7: Calcd. (%): C, 41.23; H, 5.43;

N, 17.17. Found (%): C, 41.15; H, 5.44; N, 17.26. FT-IR in KBr: 3282, 1589, 1437, 1358, 1117, 755, 623 cm^-1. ¹H-NMR (400 MHz, D2O) δ^ppm: 4.08-4.13 (2H), 4.27-4.34 (2H), 4.90 (2H), 5.45 (2H), 7.22-7.32 (4H), 7.69-7.76 (2H), 7.57-8.59 (2H). ¹³C-NMR (100 MHz, D2O + CD3CN) δppm: 43.4, 50.2, 51.8, 58.6, 123.8, 123.9, 123.9, 124.0, 138.4, 138.5, 150.6, 150.9, 155.3 and 156.2. ESI-Mass (m+1): Calcd. 272.32; Found, 272.12.

2.4.5 Isolation of L2/

L2/

was isolated as its perchlorate salt from the reaction of complex 2.2 (0.260 g, 0.5 mmol) with NO following the procedure used for the isolation of the L1/

-perchlorate.

Yield: 0.132 g, ~70%. Elemental analyses for C15H22N5ClO6: Calcd. (%): C, 44.62; H, 5.49;

N, 17.84. Found (%): C, 42.65; H, 5.49; N, 17.91. FT-IR in KBr: 3067, 2927, 1451, 1437, 1358, 1083, 1123, 755, 629 cm^-1. ¹H-NMR (400 MHz, D2O) δ^ppm: 2.36-2.39 (2H), 3.60- 3.64 (2H), 4.32-4.35 (2H), 4.87 (2H), 5.43 (2H), 7.25-7.29 (4H), 7.70-7.73 (2H), 7.58-8.59 (2H). ¹³C-NMR (100 MHz, D2O + CD3CN) δppm: 30.2, 42.8, 50.5, 51.9, 58.4, 123.6, 123.8,

C20H22N6ClO5: Calcd. (%): C, 52.01; H, 4.80; N, 18.19. Found (%): C, 52.08; H, 4.81; N, 18.12. FT-IR in KBr: 2936, 1594, 1438, 1118, 1087, 630 cm^-1. ¹H-NMR (400 MHz, D2O) δppm: 3.81 (2H), 4.46 (2H), 4.93 (4H), 5.27 (2H), 7.14-7.19 (3H), 7.36-7.37 (2H), 7.53-7.62 (3H) 7.86 (2H), 8.48 (2H). ¹³C-NMR (100 MHz, D₂O + CD₃CN) δppm: 42.8, 49.9, 50.9, 52.7, 61.0, 123.5, 123.8, 123.9, 124.1, 124.3, 124.5, 137.8, 138.1, 135.2, 150.2, 150.6, 150.9, 155.7, 156.7 and 160.5. ESI-Mass (m+1): calcd. 363.43; Found, 363.45.

2.4.7 Isolation of L4/

L4/

was isolated from the reaction of complex 2.4 (0.308 g, 0.5 mmol) with NO following the procedure used for the isolation of L3/

. Yield: 0.155 g, ~67%. Elemental analyses for C19H23N7ClO5: Calcd. (%): C, 48.67; H, 4.94; N, 20.91. Found (%): C, 48.73; H, 4.94; N, 20.83. FT-IR in KBr: 1598, 1448, 1123, 756, 630 cm^-1. ¹H-NMR (400 MHz, D2O) δppm: 2.20 (2H), 3.78 (2H), 4.26 (3H), 4.62 (4H), 5.02 (2H), 6.61 (1H), 6.80 (1H), 7.14 (2H) 7.65 (2H), 7.83 (2H), 8.46 (2H). ¹³C-NMR (100 MHz, D2O + CD3CN) δppm: 33.6, 49.0, 51.3, 51.5, 51.9, 61.0, 123.5, 123.8, 123.9, 124.4, 127.5, 137.8, 136.1, 135.4, 150.1, 150.6, 150.9, 155.6 and 160.0. ESI-Mass (m+1): Calcd. 366.43; Found, 366.37.

Chapter 2

42